1. Field of the Invention
The present invention relates to an apparatus for manufacturing a semiconductor substrate used for manufacturing SIMOX (Separation by Implanted Oxygen) substrate by implanting oxygen ions into a semiconductor substrate of silicon and the like, and then applying a high-temperature treatment.
This application claims priority from Japanese Patent Application No. 2005-244656 filed on Aug. 25, 2005, the content of which is incorporated herein by reference.
2. Background Art
In a common batch-type ion implantation apparatus, for example, as shown in Patent Reference 1, multiple pieces of semiconductor substrate are mounted on multiple support disks equipped on one rotating plat-form and processed in a lump under vacuum.
An ion accelerated by necessary energy is implanted into a semiconductor substrate while being rotated like turning these support disks. As methods for uniformly implanting an ion in a semiconductor substrate, a method of scanning the support disks themselves in conformity to the turning of support disks or a method of scanning an ion beam only by turning support disks are given. In both methods, uniform ion implantation may be performed over the entire surface of all semiconductor substrates on the support disks.
Centrifugal force is utilized for the support of semiconductor substrates. Therefore, a structure of slightly inclining support disks for supporting the semiconductor substrates to the turning surface of the support disks to press the semiconductor substrates against the support disks is adopted.
If turning is inclined at only an angle α to the turning surface of the support disks, the semiconductor substrates are pressed against the support disks by a component of the centrifugal force in proportional to sine α. The inclination α may not be increased too large in restricting the ion implantation.
Therefore, the semiconductor substrates fly off to the outside only by a frictional force at the rear of semiconductor substrates. Accordingly, members called stoppers for suppressing the fly-off of the semiconductor substrates is necessary.
These stoppers have a width, but the support disks are commonly turned at several hundred rpm or so, and the acceleration at this time is also a value of over 150 G (G: gravity acceleration). The semiconductor substrates are 12 in. in diameter and about 150 g, thus the stoppers must support a load (22.5 kg) which is 150 times as much as its own weight.
However, the semiconductor substrates may not be supported on the support disks only at peripheral contact positions by the stoppers. Substrate inner supports must also be provided for the semiconductor substrates at the inner periphery of the support disks.
Moreover, an ion beam current implanted into the semiconductor substrates must flow to the outside of the support disks and the like. Therefore, at least the stoppers or the substrate inner supports must be ensured as a current passage. Stoppers capable of ensuring contact with the semiconductor substrates by the centrifugal force are suitable for the passage of ion beam current.
Furthermore, heat generated in the semiconductor substrates due to ion implantation is put out through the support disks by radiation heat transfer from the entire rear face of the semiconductor substrates, but part of heat is also put out through the stoppers or the substrate inner supports.
In the manufacture of SIMOX substrate, absolute values of the film thickness of the SI (Silicon ON Insulator) layer and BOX (Buried Oxide) layer are decided by the acceleration voltage and the implantation rate during oxygen ion implantation. At this time, the film thickness also depends upon the temperature during implantation.
The ion implantation rate may be made uniform to a level at which the uniformity of the film thickness is not affected by control of above-mentioned scanning conditions. It is also possible to ensure a uniformity level of temperature during implantation by heating the substrates with a radiation heater having an area larger than the semiconductor substrates, for which implantation is performed at the temperature during implantation, and further using material with high adiabaticity or high heat insulativity and no conductivity in the contact part of the substrate inner supports.
In an ion implantation apparatus used for manufacturing the SIMOX substrate, semiconductor substrates must be heated to a desirable temperature. Therefore, a radiation heater, such as halogen lamp and the like is disposed in a vacuum vessel provided with above-mentioned support disks.
When ion implantation is performed, the support disks loaded with the semiconductor substrates are turned and then the semiconductor substrates are heated to a desired temperature by the radiation heater. Subsequently, an ion beam is raised to perform ion implantation while controlling the disks or scanning of the beam.
If the implantation rate reaches a set value for the entire surface of semiconductor substrates, the scan control is stopped at a position where the ion beam does not hit the semiconductor substrates, the radiation heater is cut off and the rotation of the support disks is stopped.
Recently, however, the SOI layer has tended to be extremely thinned in the SOI substrates including SIMOX and only slight non-uniformity of film thickness has not been allowed. As a result, the problem that prescribed film thickness uniformity could not be realized was known to arise in the prior art.
In view of the above problem, an object of the present invention is to provide an apparatus for manufacturing semiconductor substrates capable of forming a SOI layer and BOX layer in a uniform thickness as a whole.
(Patent Reference 1) Japanese Patent Application, Publication No. 2002-231176